1. Field of the Invention
The present invention relates to an electron emitting apparatus and, more particularly, to an electron emitting apparatus in which the electron emission is induced by applying a voltage. Such an electron emitting apparatus is preferably used as an electron beam generating source of an electron beam applied apparatus such as, e.g., an electron beam exposing apparatus or the like.
2. Related Background Art
Hitherto, the thermion emission from a hot cathode has been used as an electron generating source. Such an electron emission using the hot cathode has problems such that the amount of energy loss by the heating is large, it is necessary to form the heating means, it takes a long time to preheat, and the system is likely to become unstable by the heat.
To solve these problems, the electron emitting device without the aid of the heating has been studied and several types of devices have been proposed.
For example, the following devices have been proposed: a device of the type such that an avalanche breakdown phenomenon is caused by applying a reverse bias voltage to the PN junction, thereby emitting the electrons to the outside of the device; a device of the (MIM) type such that it has a structure of metal-insulating material layer-metal layer and by applying a voltage between both metals, the electrons passed through the insulating material layer are emitted from the metal layer to the outside of the device by the tunnel effect; a device of the surface conductivity type such that by applying a voltage to a high resistance thin film in the direction perpendicular to the direction of film thickness, the electrons are emitted from the surface of the thin film to the outside of the device; a device of the field effect (FE) type such that by applying a voltage to the metal having such a shape that the field concentration easily occurs, the electric field of a high density is locally generated, thereby emitting the electrons from the metal to the outside of the device; and the like.
As an example of application of those electron emitting devices, there is considered a method whereby an electron emitting apparatus is constituted by arranging a plurality of electron emitting devices and the ON-OFF operation of the emission of the electrons from each device is controlled, thereby allowing the electrons to be emitted like a desired pattern and to collide with the surface of a workpiece, and thereby working the surface or changing the surface quality by the exposure of an electron beam.
As the foregoing electron emitting apparatus, there is considered an apparatus in which electron emitting devices are two-dimensionally arranged. According to such an electron emitting apparatus, the workpiece is merely arranged to face this apparatus and each electron emitting device is ON-OFF controlled in this state, thereby enabling the electron beam exposure of the surface of the workpiece to be performed like a two-dimensional pattern.
However, in the foregoing electron emitting apparatus, it is difficult to use the whole surface of the electron emitting device in order to emit the electrons because of the constitution of each device. Therefore, the two-dimensional pattern for the emission of the electrons is a dot matrix pattern in which a space exists between dots and there is a drawback such that a continuous pattern cannot be formed.